Field of the Invention
The present invention relates to methods for producing a printed wiring board. The present invention also relates to printed wiring board produced by such a method.
Discussion of the Background
As a technique of producing a printed wiring board, there is known a production method using a build-up process of alternately layering insulating layers and conductive layers. In the production method using the build-up process, an insulating layer is usually formed by thermally curing a resin composition. For example, WO 2010/35451, which is incorporated herein by reference in it is entirety, discloses a technique of forming an insulating layer by: laminating a resin composition layer containing silica particles onto an internal layer substrate using an adhesive sheet including a support and the resin composition layer provided on the support; thermally curing the resin composition layer; and then subjecting the cured product to a roughening treatment.
With the demand for further densification of circuit wirings, there is a tendency toward an increase in the number of stacked layers of a build-up printed wiring board. However, as the number of stacked layers increases, the occurrence of cracks and circuit distortion due to the difference in thermal expansion between the insulating layers and conductive layers becomes a problem. As a technique for suppressing the problem of cracks and circuit distortion, for example, JP-A-2010-202865, which is incorporated herein by reference in its entirety, discloses a technique of forming an insulating layer with a low thermal expansion coefficient by increasing the content of an inorganic filler such as silica particles in the resin composition.
In the technique described in WO2010/35451, silica particles on the surface of the cured product are detached in the roughening treatment, which allows an insulating layer having sufficient peel strength with respect to a conductive layer to be achieved. However, when using a resin composition having a high content of inorganic filler such as silica particles in order to form an insulating layer with a low thermal expansion coefficient, a reduction in peel strength between the formed insulating layer and conductive layer may be unavoidable even using the above technique.
In the production of a printed wiring board, an insulating layer may be formed by thermally curing a resin composition layer in a state such that a support is attached to the resin composition layer, from the viewpoint of the smoothness of the resultant insulating layer and from the viewpoint of masking when via-holes are formed. Particularly in such case, the present inventors have found that, when using a resin composition having a high content of inorganic filler, the reduction in peel strength between the formed insulating layer and conductive layer tends to be significant.
Thus, there remains a need for improved methods for producing a printed wiring board.